Ceramium barrowense Huisman

Scientific Description

Habit and structure. Thallus pale red, with darker nodes; prostrate axes attached by rhizoids arising from periaxial cells; erect branches simple to once-branched, arising from the nodes. Prostrate axes spreading for several millimetres, with axial cells 35–50 µm diam. [L:B 2.5–3.5]; nodes 50–55 µm diam. Attachment rhizoids 1–3 per node, simple or rarely branched, 1–3-celled, hyaline, to 50 µm long, 25–30 µm diam., shorter and with digitate ends when growing on a firm host. Erect axes to 1.3 mm tall, with cells to 35–50 µm diam.; L:B up to 6 in lower portions, shorter distally. Apices straight to slightly curved. Nodal cortication with 5 or 6 periaxial cells, each cutting off 2 cells acropetally and basipetally, these generally dividing further to form a corticating band with 3–6 layers; acropetal and basipetal development mostly equal or with basipetal cells slightly larger.

Reproduction. Spermatangia arising on outer cells of nodal cortication near branch apices, the nodes remaining discrete or forming a stichidium-like structure. Carpogonial branches and carposporophytes formed near apices of erect axes, displaced laterally by continued growth of the bearing branch. Mature carposporophytes with 1 or 2 spherical gonimolobes to 110 µm diam., partially surrounded by 3 or 4 involucral branches of similar form to vegetative branches. Tetrasporangia formed in whorls of up to 5 on the lower 4 or 5 nodes of erect branches, the nodes remaining discrete and not becoming confluent, tetrahedrally divided, 50–60 × 40–45 µm, partially covered by nodal cells (to c. 30–50% of the sporangia), with a thick wall that also covers the subtending nodal cells. Nodal cortication associated with tetrasporangia to 75 µm wide.

Distribution. Known only from Barrow Island and from the Maret Islands, north-western Australia, but probably widespread in the region.

Habitat. Epiphytic on Codium and Galaxaura in the intertidal and shallow subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 389–391 (2018)]